Straddle carrier are vehicles with very large ground clearances that can be used to lift heavy loads. This is typically accomplished by positioning the straddle carrier over the item that needs to be lifted. In order for an item to be straddled in this manner, it must be shorter than the ground clearance of the carrier and narrower than the distance between the wheels. The item may then be raised up by a winch, block and tackle type device, or lifting forks. Early straddle carriers were used to move lumber, though modern usage is typically limited to metal objects such as cargo containers, steel billets, and heavy equipment.
The first straddle carriers appeared in the early part of the 20th century and were primarily used in the lumber industry. Some of the earliest units were capable of lifting about 12,000lbs (about 5,443kg) and were powered by electricity. Many of the early straddle carriers had only two wheel steering and used open cabs, if they had one at all. Later units used automobile engines and could lift heavier loads.
Modern straddle carriers come in a wide variety of configurations for usage in different industries. Enclosed cabs are common, and many units have heating and cooling options to make the operator more comfortable. Four wheel drive and four wheel steering is also common. The wheels of a straddle carrier often cannot be turned very sharply due to the presence of the item that is being carried, so the ability to turn all four wheels at once can result in a more acceptable turning radius. Some units can lift over 100,000lbs (45,000kg) and move at speeds of about 19mph (30kph).
One major use for the straddle carrier is at ports and shipping yards. Specialized carriers can straddle large shipping containers and stack them up to four units high. Some of the tallest straddlers are used for this purpose, since standard cargo containers are each eight feet (about 2.4 meters) tall. These carriers can be instrumental in the logistics of moving shipping containers around a port so that they can be stored and loaded onto ships, trailers, or trains.
Straddle carriers can also be useful in a number of other situations. Steel billets are often moved via straddle carrier, and various industries also use these vehicles to transport heavy equipment around job sites. The petrochemical industry often uses them to move heat exchangers and other bulky equipment. Any item that is too heavy or cumbersome to be moved by a conventional forklift or other vehicle can typically be transported by straddle carrier if it will fit between the legs.